1. Field of the Invention
The present invention relates to an automatic balance adjusting centrifuge, and particularly to an automatic balance adjusting centrifuge compensating for the imbalance of the centrifugal force by transferring balance weights equipped in rotating arms.
2. Description of the Related Art
As is well known, a centrifuge is an essential equipment which is widely used over medical and physiochemical fields, and is an instrument which separates sample elements by rotating a rotor equipped with buckets containing samples at a high speed to provide the samples with high centrifugal acceleration. Thus, high density elements in the samples are placed at the outer layer along the radial direction of the rotor and low density elements in the samples are placed at the inner layer along the radial direction.
In the operation of the centrifuge, imbalance of the centrifugal force is inevitably created by the weight differences among buckets due to the discrepancy in the number of samples within each bucket or in the total weight. However, the conventional centrifuge without the automatic balancing function brought about a problem of imposing the laborious works on users, such as measuring the weight of each sample manually to load the samples with an identical weight on a rotor symmetrically.
To address this problem, the applicant has already suggested several automatic balance type centrifuges and reserved the rights in United States as patents. To be concrete, United States patent registration number U.S. Pat. No. 7,285,085 B2 (registered date: Oct. 23, 2007) (hereafter, it is referred to Preceding Invention; PI) discloses an automatic balance type centrifuge including a rotor, wherein the rotor comprises: a plurality of rotating arms, e.g. three rotating arms, which support buckets containing samples, have the same radial length from a rotational shaft for centrifuging, and are disposed around the rotational shaft with equal angles; a balance weight installed to be movable along the radial direction of each rotating arm so as to compensate for the imbalance induced by the centrifugal force during centrifugal separation process; and a balance weight transfer mechanism transferring each balance weight horizontally along the radial direction of each corresponding rotating arm. In PI, detection of imbalance of the centrifugal force, that is, imbalance of bucket weights, for example, can be carried out by an electronic scale which is installed in separate from the rotor and goes up and down in the lower part of each bucket.
FIGS. 1, 2, and 3 are perspective view of a rotor of a centrifuge proposed in the PI, exploded view, and the cross-sectional view, respectively. As shown in FIG. 1 through FIG. 3, the rotor of the centrifuge of the PI can comprise the three rotating aims 29 supporting sample-loaded buckets 31, a balance weight 15 installed in each rotating arm 29 to compensate for the weight imbalance of the rotor during the centrifuging process, and a balance weight transfer mechanism transferring the balance weight 15 along the radial direction of each rotating arm 29.
In the configuration described in the above, the rotating arm 29 can be formed by cutting away some portion equi-angularly, which is supposed to install buckets 31, from a disk with a prescribed thickness, and in the present preferred embodiment, each rotating arm 29 maintains 120.degree. interval with each other. And at both sides of each rotating arm 29, bucket supporting pins 33 are formed to support the buckets 31 to be assembled so that adjacent rotating arms 29 cooperate to support the buckets 31.
Meanwhile, in each rotating arm 29, a slot 29a is formed along the radial direction to guides the balance weight 15 to be transferred along the horizontal direction, and is preferably implemented as a rectangle-type long groove. The balance weight 15 is preferably implemented as the form of hexahedron in order not to be rotated in the slot 29a, and has the female screw (not illustrated) formed in the center.
Each balance weight transfer mechanism can comprise a balance weight transfer motor 5 installed at the center part of the rotor, whose shaft is in the line of the vertical axis; a worm 7 coupled with the end of the shaft of the balance weight transfer motor 5 by shaft coupling; a balance weight transfer shaft 17 which is installed in a longitudinal direction within the slot 29a and of which an outer circumferential surface a male screw is formed on to couple with a female screw of the balance weight 15 by screwed connection; a worm gear 19 coupled with the worm 7 by gear coupling and also coupled with one end of the balance weight transfer shaft 17 by shaft coupling; a thrust bearing 21 and a radial bearing 23 which are coaxially coupled with each end of the balance weight transfer shaft 17 respectively.
Meanwhile, in transferring the balance weight 15 horizontally within the slot 29a, a position sensor 13, preferably a limit switch, is required to sense the fixed reference position, and the position sensor 13 may be installed at proper position of the slot 29a, preferably at a support bracket 11 installed by extending downward from a balance weight cover 9 (slot cover 9). Non-described reference numbers 3 and 1 in the figures indicate a supporting frame to support the balance weight transfer motor 5 and a motor cap 1 to cover the top of the supporting frame 3, respectively, and another non-described reference number 9 indicates a slot cover to cover the top of the slot 29a. The reference number 25 and 27, respectively, indicate housings to fix a thrust bearing 21 and a radial bearing 23 inside the slot 29a. 
However, in the conventional automatic balance adjusting centrifuge as described in the above, there has been a difficulty of designing/manufacturing for enhancing the contact ratio of tooth surface between a worm and a rack-type worm wheel, because it uses a worm shaft-coupled with a balance weight transfer motor, a worm gear tooth-coupled with the worm, and a balance weight transfer shaft coaxial-coupled with the worm gear, as balance weight transferring means.
Furthermore, there have been some problems such that accuracy falls down because of analogizing the current position of a balance weight with the number of rotation of the balance weight transfer motor implemented simply by a step motor, structure is complicated because of separating a balance weight transfer shaft from a motor shaft, and the efficiency of space utilization is low because of installing the balance weight transfer motor as the shaft faces to vertical direction.